Aqueous surface conditioner and surface conditioning method for phospating treatment

ABSTRACT

An aqueous surface conditioner for use in a phosphating treatment is provided which contains crystals having an average diameter of 5 μm or less in an amount of at least 0.1 g/L. The crystals are selected to have a two-dimensional epitaxy that matches within 3% of misfit with the crystal lattice of one phosphate coating selected from among (1) hopeite/Zn 3 (PO 4 ) 2 .4H 2 O) and/or phosphophyllite (Zn 2 Fe(PO 4 ) 2 .4H 2 O), (2) scholzite (CaZn 2 (PO 4 ) 2 .2H 2 O) and (3) hureaulite (Mn 5 (PO 4 ) 2 [PO 3 (OH] 2 .4H 2 O).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an aqueous surface conditionerfor use in a phosphate coating treatment performed on the surface of ametal material such as a sheet of iron, steel, zinc-plated steel, oraluminum in order to promote the chemical conversion reaction andshorten the duration thereof and to achieve greater fineness of thecrystals that make up the phosphate coating. The invention also relatesto a method for the surface conditioning of a metal material.

[0003] 2. Discussion of the Related Art

[0004] The formation of fine and closely-spaced phosphate coatingcrystals on a metal surface has become necessary today in order toimprove corrosion resistance after painting in the phosphatingtreatments performed on automobiles and to extend the life of pressingmolds or reduce friction during pressing in phosphating treatments usedfor plastic working. In view of this, a surface conditioning step iscarried out prior to a phosphate coating chemical conversion step forthe purpose of activating the metal surface so that fine andclosely-spaced phosphate coating crystals will be obtained and creatingnuclei for the deposition of phosphate coating crystals. The followingis a typical example of a phosphate coating chemical conversion processperformed in order to obtain fine and closely-spaced phosphate coatingcrystals.

[0005] (1) degreasing

[0006] (2) multi-stage water rinsing

[0007] (3) surface conditioning

[0008] (4) phosphate coating chemical conversion treatment

[0009] (5) multi-stage water rinsing

[0010] (6) pure water rinsing

[0011] Surface conditioning is performed in order to make phosphatecoating crystals finer and more closely-spaced. Compositions with thisaim have been discussed in U.S. Pat. Nos. 2,874,081, 2,322,349, and2,310,239, for example, and examples of the main constituent componentsof the surface conditioner include titanium, pyrophosphoric acid ions,orthophosphoric acid ions, and sodium ions. The above-mentioned surfaceconditioning compositions are called “Jernstedt salts,” and titaniumions and titanium colloids are included in aqueous solutions thereof. Ametal that has been degreased and rinsed with water is immersed in anaqueous solution of one of the above-mentioned surface conditioningcompositions, or a phosphating treatment surface conditioner is sprayedonto the metal, causing the titanium colloid to be adsorbed to the metalsurface. The adsorbed titanium colloid forms the nuclei for phosphatecoating crystal precipitation in the subsequent phosphate coatingchemical conversion step, which promotes the chemical conversionreaction and makes the phosphate coating crystals finer and moreclosely-spaced. All of the surface conditioning compositions inindustrial use today make use of Jernstedt salts. Various problems havebeen encountered, however, when a titanium colloid obtained from aJernstedt salt is used in a surface conditioning process.

[0012] The first of these problems is that the phosphating treatmentsurface conditioner deteriorates over time. When a conventional surfaceconditioning composition is used, this composition is extremelyeffective in terms of making the phosphate coating crystals finer moreclosely-spaced immediately after an aqueous solution is produced.However, the titanium colloid agglomerates a few days after the aqueoussolution is prepared. The phosphating treatment surface conditionerloses its effect within this time regardless of whether it has been usedor not, and the phosphate coating crystals that are obtained end upbeing coarse.

[0013] Japanese Laid-Open Patent Application S63-76883 proposes a methodfor measuring the average particle diameter of the titanium colloid in aphosphating treatment surface conditioner, continuously discarding thephosphating treatment surface conditioner so that the average particlediameter will be less than a specified value, and supplying freshsurface conditioning composition in an amount corresponding to thediscarded amount, thereby maintaining the surface conditioning effect ata constant level. However, while this method does allow the effect ofthe phosphating treatment surface conditioner to be maintainedquantitatively, the phosphating treatment surface conditioner has to bediscarded for the effect to be maintained. Also, a large quantity ofphosphating treatment surface conditioner must be discarded with thismethod in order to keep the effect of the phosphating treatment surfaceconditioner at the same level as when the aqueous solution was firstproduced. Therefore, in actual practice, the wastewater treatmentcapacity of the plant where this method is used also comes intoquestion, so the effect is maintained through a combination ofcontinuous discarding and complete replacement of the phosphatingtreatment surface conditioner.

[0014] The second problem is that the effect and service life of aphosphating treatment surface conditioner are greatly affected by thehardness of the water used during replenishment. Industrial water isusually used for replenishing a phosphating treatment surfaceconditioner. As is commonly known, though, industrial water containscalcium, magnesium, and other such cationic components that are thesource of the total hardness, although the amounts contained can varygreatly depending on the source of the industrial water. It is knownthat the titanium colloid that is the main component of a conventionalphosphating treatment surface conditioner takes on an anionic charge inan aqueous solution, and the electrical repulsion thereof disperses thecolloid and keeps it from settling. Therefore, if cationic componentssuch as calcium or magnesium are present in large quantity in industrialwater, the titanium colloid will be electrically neutralized by thecationic components, the repulsive force will be lost, agglomeration andsettling will occur, and the effect of the colloid will be lost.

[0015] In view of this, a method has been proposed in which a condensedphosphate such as a pyrophosphate is added to a phosphating treatmentsurface conditioner for the purpose of sequestering the cationiccomponents and maintaining the stability of the titanium colloid.Unfortunately, when a large quantity of condensed phosphate is added toa phosphating treatment surface conditioner, the condensed phosphoricacid reacts with the surface of a steel sheet and forms an inert film,which results in poor chemical conversion in the subsequent phosphatecoating chemical conversion process. Also, in locales where the calciumor magnesium content is extremely high, purified water must be used forsupplying and replenishing the phosphating treatment surfaceconditioner, which is a major drawback in terms of cost.

[0016] The third problem is that the temperature and pH are limited intheir range. Specifically, if the temperature is over 35° C. and the pHis outside a range of 8.0 to 9.5, the titanium colloid will agglomerateand lose its surface conditioning effect. Therefore, the predeterminedtemperature and pH range must be used with a conventional surfaceconditioning composition, and the surface conditioning compositioncannot be added to a degreasing agent or the like so that the effect ofcleaning and activating a metal surface will be obtained with a singleliquid over an extended period of time.

[0017] The fourth problem is that there is a limit to how fine phosphatecoating crystals can be made through the effect of a phosphatingtreatment surface conditioner. The surface conditioning effect isobtained by causing the titanium colloid to adsorb to a metal surfaceand form the nuclei during phosphate coating crystal precipitation.Therefore, the more titanium colloid particles are adsorbed to the metalsurface in the surface conditioning step, the finer and moreclosely-spaced the resulting phosphate coating crystals will be. Themost obvious way to achieve this would be increase the number oftitanium colloid particles in the phosphating treatment surfaceconditioner, that is, raise the titanium colloid concentration. When theconcentration is increased, however, there is an increase in thefrequency of collision between the titanium colloid particles in thephosphating treatment surface conditioner, and these collisions causethe titanium colloid to agglomerate and settle. The upper limit to theconcentration of titanium colloids currently being used is 100 ppm orless (as titanium in the phosphating treatment surface conditioner), andit has been impossible to make phosphate coating crystals finer byincreasing the titanium colloid concentration over this level.

[0018] In view of this, Japanese Laid-Open Patent ApplicationsS56-156778 and S57-23066 disclose a surface conditioning method in whicha suspension containing an insoluble phosphate of a divalent ortrivalent metal is sprayed under pressure onto the surface of a steelstrip as a surface conditioner other than a Jernstedt salt. With thissurface conditioning method, however, the effect is only realized whenthe suspension is sprayed under pressure onto the target material, sothis method cannot be used for surface conditioning in a phosphatecoating chemical conversion treatment performed by ordinary dipping orspraying.

[0019] Japanese Patent Publication S40-1095 discloses a surfaceconditioning method in which a zinc plated steel sheet is dipped in ahigh-concentration suspension of an insoluble phosphate of a divalent ortrivalent metal. The examples given for this method, however, arelimited to a zinc plated steel sheet, and obtaining a surfaceconditioning effect requires the use of a high-concentration insolublephosphate suspension of no less than 30 g/L.

[0020] Therefore, even though various problems associated with Jernstedtsalts have been indicated, so far no one has proposed a new technique toreplace them.

[0021] Also, because the mechanism by which these salts act is notclear, it is uncertain on which substances these salts will have asurface conditioning effect, and searching for these substances entaileda tremendous amount of labor.

SUMMARY OF THE INVENTION

[0022] It is an object of the present invention to solve theabove-mentioned problems and provide a novel phosphating treatmentsurface conditioner that has excellent stability over time and is usedto promote the chemical conversion reaction and shorten the durationthereof in a phosphate coating chemical conversion treatment, and toreduce the size of the resulting phosphate coating crystals.

[0023] The inventors examined means for solving the above problems, andclosely studied the mechanism by which surface conditioners function.This led to the discovery that in the course of producing a phosphatecoating, the coating components reach a state of supersaturation as themetal dissolves. The most important effect of a surface conditioner isthat the crystals it produces function as nuclei for phosphate coatingcrystals. The performance of a surface conditioner is determined by howeffectively it can act as crystal nuclei. In other words, the inventorsfound that crystals with a lattice constant close to that of phosphatecoating crystals function as pseudo-crystal nuclei, resulting in asurface conditioning effect. Further research in this area led to theperfection of the present invention.

[0024] Specifically, the present invention relates to an aqueous surfaceconditioner for use in a phosphating treatment, which contains crystalshaving an average diameter of 5 μm or less in an amount of at least 0.1g/L, said crystals having a two-dimensional epitaxy that matches within3% of misfit with the crystal lattice of one phosphate coating selectedfrom among (1) hopeite (Zn₃(PO₄)₂.4H₂O) and/or phosphophyllite(Zn₂Fe(PO₄)₂.4H₂O), (2) scholzite (CaZn₂(PO₄)₂.2H₂O), and (3) hureaulite(Mn₅(PO₄)₂[PO₃(OH)]₂.4H₂O).

BRIEF DESCRIPTION OF THE DRAWINGS

[0025]FIG. 1 is a concept diagram in which a LaMer diagram is applied toa surface conditioner (crystal growth steps);

[0026]FIG. 2 shows the unit crystal lattices for hopeite (zincphosphate) and magnesium hydrogenphosphate; and

[0027]FIG. 3 is a diagram in which unit crystal lattices of hopeite havebeen arranged, with the grid-shaped solid line portion being a view ofthese crystal lattices viewed perpendicular to the (020) plane, and thedashed line portion being the unit crystal lattices of magnesiumhydrogenphosphate arranged over these.

DETAILED DESCRIPTION OF THE INVENTION

[0028] In terms of how they are produced, phosphate coating crystals canbe described by a LaMer diagram that shows the process in which crystalsprecipitate from a solution as a result of increased concentration. Ingeneral, as the solute concentration rises, crystal precipitation willnot occur as soon as the saturation concentration is exceeded, andcrystal production occurs only when the crystal nucleus productionconcentration C*_(min) is reached, after which the crystals grow, so thesolute concentration decreases. Phosphate coating crystals are believedto precipitate through the same process, and this corresponds to when nosurface conditioner is used (corresponds to the solid line portion inFIG. 1). In this case, crystal nuclei are produced only in the shadedarea in FIG. 1. Because there are few crystal nuclei, the crystalcoating is often coarse, and it takes a long time for the coatingproduction reaction to conclude.

[0029] In contrast, when a surface conditioner is used, because thetitanium colloid particles or the like that constitute this componentfunction as pseudo-nuclei for the phosphate coating crystals, crystalgrowth already begins at a concentration C*x that is lower than thecrystal nucleus production concentration C*_(min). In this case, thenumber of crystal nuclei is determined by the number of titanium colloidparticles or the like contained in the surface conditioner, soclosely-spaced coating crystals can be produced by increasing the numberof these particles. As shown in FIG. 1, the coating crystals areproduced in a short time, so the phosphate chemical conversion treatmentdoes not take as long. Here, the closer the concentration C*_(x) atwhich crystal growth commences on the pseudo-crystal nuclei is to thesaturation concentration C_(S), the less time it will take to producethe coating, so efficiency is higher.

[0030] Because of all this, substances capable of become pseudo-crystalnuclei in a surface conditioner were closely examined.

[0031] As a result, it was confirmed that when the phosphate coating iscomprised mainly of hopeite and/or phosphophyllite, a surfaceconditioning effect will be observed with crystals of magnesium hydrogenphosphate (MgHPO₄ .3H₂O), zirconium oxide (ZrO₂), zinc oxalate(Zn(COO)₂), cobalt oxalate (Co(COO)₂), iron orthosilicate (Fe₂SiO₄),iron metasilicate (FeSiO₃), and magnesium borate (Mg₃(BO₃)₂); when thephosphate coating is comprised mainly of scholzite, this effect will beobserved with crystals of anhydrous cobalt phosphate (CO₃(PO₄)₂),anhydrous zinc phosphate (γ-Zn₃(PO₄)₂), anhydrous zinc magnesiumphosphate (Zn₂Mg(PO₄)₂), anhydrous zinc cobalt phosphate(γ-Zn₂Co(PO₄)₂), and anhydrous zinc iron phosphate (γ-Zn₂Fe(PO₄)₂); andwhen the phosphate coating is comprised mainly of hureaulite, thiseffect will be observed with crystals of calcium orthosilicate(Ca₂SiO₄.H₂O), calcium metaphosphate (Ca₃(PO₃)₆.10H₂O), andmanganese(II) metaphosphate (Mn₃(PO₃)₆.10H₂O). The term “mainly” as usedabove means that the hopeite and/or phosphophyllite; scholzite; orhureaulite accounts for at least 50 mass %, and preferably at least 70mass %, of the phosphate coating. These surface conditioning substancescan be used singly or in combinations of two or more types according tothe corresponding phosphate coating.

[0032] The inventors turned their attention to the lattice constant ofthe crystals of these surface conditioning substances, and found it tobe close to the lattice constant of the phosphate coating crystals. Ifthe crystal structures are similar, this means that these substanceswill be effective as pseudo-crystal nuclei; this is known as epitaxy.

[0033] Manmade rain is often given as an example of epitaxy. When amicropowder of silver bromide is scattered in water vapor that issupersaturated and supercooled, the silver bromide becomes the nucleifor the growth of ice crystals, resulting in rain. This phenomenonoccurs because the lattice constant of the silver bromide crystals isextremely close to the lattice constant of ice, and the growth on onetype of crystal of a different type of crystal with a similar latticeconstant is known in the semiconductor field as epitaxial growth.

[0034] The inventors noted a surface conditioning effect in manydifferent substances, and as a result learned that, as mentioned above,a substance that has a surface conditioning effect on a phosphatecoating is a substance whose epitaxy closely matches that of thephosphate coating crystals.

[0035] The matching of epitaxy will now be discussed in detail.

[0036]FIG. 2 shows the unit lattice of hopeite (Zn₃(PO₄)₂.4H₂O). Thegrid-shaped solid line portion in FIG. 3 is a view of these crystallattices arranged and viewed perpendicular to the (020) plane. Thedashed line portion in FIG. 3 illustrates the unit lattices of magnesiumhydrogenphosphate (MgHPO₄.3H₂O) arranged over these, and the latticesmatch up well. Actually, zinc phosphate is deposited over magnesiumhydrogenphosphate, and as long as there is a good match between thelattices as above, the crystals will seat well and grow readily. Thereis a certain amount of lattice misalignment in this example as well, andthis is called misfit. In this example, the a axis of the zinc phosphateversus the b axis of the magnesium hydrogenphosphate is10.6845/10.6067Å=1.0073, so the misfit is 0.7%. Similarly, the c axis ofthe magnesium hydrogenphosphate versus double the c axis of the zincphosphate is 10.0129/(5.0284×2)=0.9956, so the misfit is −0.4%.

[0037] Naturally, the smaller the misfit, the better the match betweenthe crystal lattices. What should be noted here is that the integermultiples of one lattice constant may also match another, and all planecombinations must be taken into account.

[0038] If we thus calculate the misfit in a two-dimensional plane forall plane combinations, we find that substances with a surfaceconditioning effect all have a two-dimensional misfit within 3%.

[0039] Table 1 is an example of calculating the misfit for theabove-mentioned surface conditioning substances used when a zincphosphate coating is hopeite and/or phosphophyllite (Zn₂Fe(PO₄)₂.4H₂O).The two-dimensional misfit was within 3% in every case, and a surfaceconditioning effect was observed.

[0040] Furthermore, no surface conditioning effect was observed withsubstances in which the misfit was over 3%.

[0041] It is known that a zinc phosphate coating contains not onlyhopeite but also a large amount of phosphophyllite. Phosphophyllite hasa crystal structure that is extremely similar to that of hopeite, andthe crystal lattices are also very close, so the two precipitate asmixed crystals.

[0042] The above description of epitaxy was for when a zinc phosphatecoating is produced, but the same applies to when the coating producedis scholzite or hureaulite. The misfit should be calculated by takinginto account all possible arrangement combinations of the crystallattice of scholzite or hureaulite instead of the crystal lattice of thezinc phosphate shown in FIG. 2.

[0043] Table 2 is an example of calculating the misfit for theabove-mentioned surface conditioning substances used when a zincphosphate coating is scholzite. The two-dimensional misfit was within 3%in every case, and a surface conditioning effect was observed when ascholzite coating was produced.

[0044] Table 3 is an example of calculating the misfit for theabove-mentioned surface conditioning substances used when a zincphosphate coating is hureaulite. The two-dimensional misfit was within3% in every case, and a surface conditioning effect was observed whenhureaulite was produced.

[0045] It is preferable for the two-dimensional misfit to be within2.5%, whether with (1) hopeite and/or phosphophyllite, (2) scholzite, or(3) hureaulite.

[0046] The average diameter of the crystals of these surfaceconditioning substances must be no more than 5 μm, and 1 μm or less ispreferable. The surface conditioning effect will be weak if the averagediameter is over 5 μm.

[0047] There are no particular restrictions on the concentration ofthese crystals in the surface conditioner of the present invention, butthe crystals must be contained in an amount of at least 0.1 g/L, with0.1 to 50 g/L being preferable, and 1 to 5 g/L being even better. Thesurface conditioning effect will be inadequate if the amount is lessthan 0.1 g/L, but no further effect will be obtained by exceeding 50g/L, so this would merely be a waste of money.

[0048] Another essential component of the surface conditioner of thepresent invention is water. This water may be purified water, tap water,or industrial water. The above-mentioned surface conditioning substancesare usually suspended in water. If needed, a dispersant may be used tosuspend the substances.

[0049] A monosaccharide, oligosaccharide, polysaccharide, etherifiedmonosaccharide, etherified oligosaccharide, etherified polysaccharide,water-soluble macromolecular compound, or the like can be used as adispersant. Examples of monosaccharides include glucose, fructose,mannose, galactose, and ribose; examples of oligosaccharides includesucrose, maltose, lactose, trehalose, and maltotriose; examples ofpolysaccharides include starch, dextrin, dextran, and glycogen; examplesof etherified monosaccharides, oligosaccharides, and polysaccharidesinclude compounds obtained by etherifying the hydroxyl groups of theconstituent monosaccharides with substituents such as —NO₂, —CH₃,—C₂H₄OH, —CH₂CH(OH)CH₃, and —CH₂COOH; and examples of water-solublemacromolecular compounds include polyvinyl acetate, partially hydrolyzedpolyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol derivatives(such as cyanoethylated acrylonitrile, acetalated formaldehyde,urethanated urea, and derivatives in which carboxyl groups, sulfonegroups, amide groups, or the like have been introduced), and copolymersof vinyl acetate with copolymerizable monomers (such as acrylic acid,crotonic acid, and maleic anhydride).

[0050] There are no particular restrictions on the concentration of thedispersant as long as the amount is sufficient to disperse the crystalsused in the present invention, but the concentration is usually 1 to2000 ppm.

[0051] The material to be conditioned with the surface conditioner ofthe present invention is any metal material that will undergo aphosphate chemical conversion treatment, examples of which includesteel, zinc and zinc plated materials, materials plated with zincalloys, aluminum and aluminum plated materials, and magnesium.

[0052] The surface conditioner of the present invention is usuallyapplied after the metal material has been degreased and rinsed withwater, but this is not necessarily the case. The surface conditioningperformed with the surface conditioner of the present invention isperformed by bringing this conditioner into contact with the surface ofa metal material for at least 1 second. More specifically andpreferably, the metal material is either immersed in the conditioner forabout 10 seconds to 2 minutes, or the conditioner is sprayed onto themetal material for about 10 seconds to 2 minutes. This treatment isordinarily carried out with the surface conditioner at normal ambienttemperature (i.e., about 15° C. to about 30° C.), but can be carried outat anywhere between normal temperature and about 80° C. Any of a greatnumber of substances can be selected with the present invention asdictated by the intended application, so it is also possible to dispersethese crystals in a degreasing agent, and perform the degreasing andsurface conditioning at the same time. In this case the treatment isusually performed by immersion or spraying for about 1 to 3 minutes at50 to 80° C.

EXAMPLES

[0053] Next, examples and comparative examples will be used to describein detail the effect of applying the phosphating treatment surfaceconditioner of the present invention. A zinc phosphate-based treatmentfor automobiles is given as an example of a phosphating treatment, butthe applications of the aqueous surface conditioner for use in aphosphating treatment pertaining to the present invention are notlimited to this example. All instances of “%” below indicate mass %.

[0054] Test Sheets

[0055] The abbreviations for an descriptions of the test sheets used inthe examples and comparative examples are given below.

[0056] SPC: cold rolled steel sheet, JIS G 3141

[0057] EG: double-sided electrogalvanized steel sheet, plating basisweight: 20 g/m²

[0058] Al: aluminum sheet, JIS 5052

[0059] Alkali Decreasing Solution

[0060] FAINCLEANA L4460 (registered trademark of Nihon Parkerizing Co.,Ltd.) was diluted to 2% with tap water and used in both the examples andthe comparative examples.

[0061] Zinc Phosphate Treatment Solution

[0062] PALBOND L3020 (registered trademark of Nihon Parkerizing Co.,Ltd.) was diluted with tap water, adjusted to a component concentrationof 4.8%, 23 point total acidity, 0.9 point free acidity, and 3 pointaccelerator, and used in both the examples and the comparative examples(these concentrations are commonly used today in automotive zincphosphate treatments).

[0063] The overall treatment process will now be discussed.

[0064] Treatment Steps

[0065] (1) alkali degreasing, 42° C., spraying for 120 seconds

[0066] (2) water rinsing, room temperature, spraying for 30 seconds

[0067] (3) surface conditioning, room temperature, immersion for 20seconds

[0068] (4) zinc phosphate treatment, 42° C., immersion for 120 seconds

[0069] (5) water rinsing, room temperature, spraying for 30 seconds

[0070] (6) deionized water rinsing, room temperature, spraying for 30seconds

[0071] Surface Conditioner

[0072] The method for preparing the phosphating treatment surfaceconditioner used in the examples will now be discussed.

Example 1

[0073] A magnesium hydrogenphosphate (MgHPO₄.3H₂O) reagent waspulverized for 60 minutes in a ball mill using zirconia beads, and thisproduct was used as a crystal powder whose epitaxy matched within 3%.This powder was suspended in purified water and then filtered through a5 μm paper filter. The magnesium hydrogenphosphate concentration wasadjusted to 5 g/L, and this product was used as a surface conditioner.

Example 2

[0074] A zinc oxalate dihydrate (Zn(COO)₂.2H₂O) reagent was baked for 1hour at 200° C. and then analyzed with an X-ray analyzer, whichconfirmed it to be zinc oxalate (Zn(COO)₂). This was pulverized for 60minutes in a ball mill using zirconia beads, and this product was usedas a crystal powder whose epitaxy matched within 3%. This powder wassuspended in purified water and then filtered through a 5 μm paperfilter. The zinc oxalate concentration was adjusted to 5 g/L, and thisproduct was used as a surface conditioner.

Example 3

[0075] A cobalt oxalate dihydrate (Co(COO)₂.2H₂O) reagent was baked for1 hour at 200° C. and then analyzed with an X-ray analyzer, whichconfirmed it to be cobalt oxalate (Co(COO)₂). This was pulverized for 60minutes in a ball mill using zirconia beads, and this product was usedas a crystal powder whose epitaxy matched within 3%. This powder wassuspended in purified water and then filtered through a 5 μm paperfilter. The cobalt oxalate concentration was adjusted to 5 g/L, and thisproduct was used as a surface conditioner.

Example 4

[0076] 12.3 g of a boric acid (H₃BO₃) reagent and 12.1 g of a magnesiumoxide (MgO) reagent were ground together in a mortar and then baked for1 hour at 1000° C. This product was analyzed with an X-ray analyzer,which confirmed it to be magnesium borate (Mg₃(BO₃)₂). Unreacted boronoxide (B₂O₃) and magnesium oxide (MgO) were detected as impurities inthis product. This was pulverized for 60 minutes in a ball mill usingzirconia beads, and this product was used as a crystal powder whoseepitaxy matched within 3%. This powder was suspended in purified waterand then filtered through a 5 μm paper filter. The magnesium borateconcentration was adjusted to 5 g/L, and this product was used as asurface conditioner.

Example 5

[0077] 10 g of zirconia sol NZS-30B made by Nissan Chemical Industries,Ltd. (a suspension containing 30% zirconium oxide fines with a diameterof 70 nm) was diluted to

[0078] 1 L and used as a crystal material whose epitaxy matched within3%. The product adjusted in this manner was used as a surfaceconditioner.

Comparative Example 1

[0079] A silicon dioxide (SiO₂) reagent was pulverized for 60 minutes ina ball mill using zirconia beads, and this product was used as a crystalpowder. This powder was suspended in purified water and then filteredthrough a 5 μm paper filter. The silicon dioxide concentration wasadjusted to 5 g/L, and this product was used as a surface conditioner.

Comparative Example 2

[0080] A magnesium oxide (MgO) reagent was pulverized for 60 minutes ina ball mill using zirconia beads, and this product was used as a crystalpowder. This powder was suspended in purified water and then filteredthrough a 5 μm paper filter. The magnesium oxide concentration wasadjusted to 5 g/L, and this product was used as a surface conditioner.

Comparative Example 3

[0081] This is an example of not using a surface conditioner.Specifically, the surface conditioning (3) was omitted from theabove-mentioned treatment steps.

[0082] Painting And Evaluation Steps

[0083] In the examples and the comparative examples, each test sheetthat had undergone the above-mentioned zinc phosphate treatment steps(1) to (6) was painted with a cationic electrodeposition paint (ELECRON2000, made by Kansai Paint) in a film thickness of 20 μm. This was bakedfor 25 minutes at 180° C., after which an intermediate coat(automotive-use intermediate coat made by Kansai Paint) was applied suchthat the intermediate coat thickness would be 40 μm, and this was bakedfor 30 minutes at 140° C. Each test sheet that had been given anintermediate coat was then given a top coat (automotive-use top coatmade by Kansai Paint) in a top coat thickness of 40 μm, which was thenbaked for 30 minutes at 140° C. The triple-coated sheet with a totalfilm thickness of 100 μm thus obtained was subjected to a saltwaterspray test.

[0084] Method For Evaluating Zinc Phosphate Coating

[0085] (1) Appearance

[0086] Each sheet was examined visually and checked for unevenness orthin paint in the zinc phosphate coating. The evaluation was given asfollows.

[0087] ⊚ uniformly good appearance

[0088] ◯ some unevenness

[0089] Δ unevenness and thin paint present

[0090] X severe thin paint

[0091] (2) Coating Weight (CW)

[0092] The mass of the treated sheet after the chemical conversion wasmeasured (referred to as W1 (g)), then the chemical conversion treatedsheet was subjected to a coating removal treatment with the stripper andstripping conditions given below, the mass of this product was measured(referred to as W2 (g)), and the coating weight was calculated usingFormula I.

[0093] With a cold rolled steel sheet

[0094] stripper: 5% chromic acid aqueous solution

[0095] stripping conditions: 75° C., 15 min., immersion stripping

[0096] With a galvanized sheet

[0097] stripper: ammonium dichromate (2 mass %)+28% aqueous ammonia (49mass %)+pure water (49 mass %)

[0098] Coating mass (g/m²)=(W1-W2)/0.021 Formula (I)

[0099] Method For Evaluating Paint Film

[0100] The paint film was evaluated by the method given below in boththe examples and the comparative examples.

[0101] (1) Saltwater Spray Test (JIS Z 2371)

[0102] An electropainted sheet in which cross-cuts had been made wassprayed for 960 hours with 5% saltwater. Upon completion of thespraying, the maximum width that peeled from the cross-cuts on one sidewas measured, and an evaluation was made.

[0103] Table 4 shows the characteristics of a chemical conversioncoating obtained in a zinc phosphate treatment using the variousphosphating treatment-use aqueous surface conditioners of the examplesand comparative examples, and shows the results of a performanceevaluation conducted after painting. A dash (-) in Table 4 means thatthe coating mass was not measured because the coating was not depositedproperly.

[0104] It was confirmed from the results in Table 4 that the phosphatingtreatment aqueous surface conditioners whose epitaxy was within 3%,which were the products of the present invention, had a surfaceconditioning effect.

[0105] On the other hand, calculation of the epitaxy for SiO₂ andhopeite (Comparative Example 1) revealed the misfit to be SiO₂(a)/hopeite (c)=4.9732/5.0284=0.989, and SiO₂ (c)/hopeite(a)=6.9236/10.6067=0.653, so the misfit was −1.1% and −34.7%.

[0106] Similarly, in Comparative Example 2, MgO (a)/hopeite(c)=4.213/5.0284=0.838, and MgO (a)×2/hopeite (a)=8.426/10.6067=0.794,so the misfit was −16.2% and −20.6%. (MgO is a cubic crystal, so onlythe a axis was used.)

[0107] Thus, it was confirmed that there was no surface conditioningeffect with the comparative examples, in which the misfit was large andthe epitaxy was different. TABLE 1 Example of calculating misfit forhopeite MgHPO₄.3H₂O Zn₃(PO₄)₂.4H₂O Misfit ZrO₂ Zn₃(PO₄)₂.4H₂O Misfit b =10.6845 a = 10.6067 +0.7% a × 2 = 10.6258 a = 10.6067 +0.2% c = 10.0129c × 2 = 10.0568 −0.4% c × sinβ = 5.0806 C = 5.0284 +1.0% Fe₂SiO₄Zn₃(PO₄)₂.4H₂O Misfit FeSiO₃ Zn₃(PO₄)₂.4H₂O Misfit b = 10.4805 a =10.6067 −1.2% c × 2 = 10.486 a = 10.6067 −1.1% a × 3 = 18.2706 b =18.3004 −0.2% a = 18.418 b = 18.3004 +0.6% Zn(COO)₂ Zn₃(PO₄)₂.4H₂OMisfit Co(COO)₂ Zn₃(PO₄)₂ .4H₂O Misfit c × 2 = 10.662 a = 10.6067 +0.5%c × 2 = 10.796 a = 10.6067 +1.8% b = 5.123 c = 5.0284 +1.9% b = 5.03 c =5.0284 +1.9% Mg₃(BO₃)₂ Zn₃(PO₄)₂.4H₂O Misfit a × 2 = 10.8028 a = 10.6067+1.8% c × 4 = 18.0284 b = 18.3004 −1.5%

[0108] TABLE 2 Example of calculating misfit for schoizite Co₃(PO₄)₂CaZn₂(PO₄)₂.2H₂O Misfit γ-Zn₃(PO₄)₂ CaZn₂(PO₄)₂.2H₂O Misfit b × 2 =16.73 a = 17.12 −2.3% b × 2 = 16.998 a = 17.12 −0.7% a × 3 = 22.671 b =22.20 +2.1% a × 3 = 22.647 b = 22.20 +2.0% γ-Zn₂(PO₄)₂ CaZn₂(PO₄)₂.2H₂OMisfit Zn₂Mg(PO₄)₂ CaZn₂(PO₄)₂.2H₂O Misfit b × 2 = 16.826 a = 17.12−1.7% b × 2 = 16.71 a = 17.12 −2.4% a × 3 = 22.608 b = 22.20 +1.8% a × 3= 22.707 b = 22.20 +2.3% γ-Zn₂Fe(PO₄)₂ CaZn₂(PO₄)₂.2H₂O Misfit b × 2 =17.08 a = 17.12 −0.2% a × 3 = 22.689 b = 22.20 +2.2%

[0109] TABLE 3 Example of calculating misfit for hureaulite Ca₂SiO₄.H₂OMn₅(PO₄)₂(HPO₄)₂.4H₂O Misfit Ca₃(PO₃)₆.10H₂O Mn₅(PO₄)₂(HPO₄)₂.4H₂OMisfit b = 9.198 b = 9.1172 +0.9% a = 9.332 c = 9.482 −1.6% a = 9.476 c= 9.482 −0.1% b = 18.13 b × 2 = 18.2344 −0.6% Mn₃(PO₃)₆.10H₂OMn₅(PO₄)₂(HPO₄)₂.4H₂O Misfit a = 9.219 b = 9.1172 +1.1% b = 17.733 a =17.618 +0.7%

[0110] TABLE 4 Type of material Example 1 Example 2 Example 3 Example 4Example 5 Comp. Ex 1 Comp. Ex 2 Comp. Ex 3 Coating SPC ⊚ ◯ ◯ ⊚ Δ X X Xappearance EG ⊚ ◯ ◯ ⊚ ◯ X X X A1 ⊚ ◯ ◯ ⊚ Δ X X X Coating weight SPC 2.12.3 2.2 2.0 2.5 — — — (g/m²) EG 2.4 2.2 2.3 2.3 2.6 — — — A1 1.7 1.6 1.61.5 1.8 — — — Saltwater spray SPC 1.0 2.0 2.5 1.0 4.0 5.0 or more 5.0 ormore 5.0 or more test of painted EG 2.0 3.5 3.0 2.5 4.0 5.0 or more 5.0or more 5.0 or more sheet (max. peel A1 0.5 or less 1.0 1.0 0.5 or less1.0 2.5 2.0 2.5 width in mm)

What is claimed is:
 1. An aqueous surface conditioner for use in aphosphating treatment comprising crystals having an average diameter of5 μm or less in an amount of at least 0.1 g/L, said crystals having atwo-dimensional epitaxy that matches within 3% of misfit with thecrystal lattice of a phosphate coating comprising one or more speciesselected from the group consisting of hopeite (Zn₃(PO₄)₂.4H₂O),phosphophyllite (Zn₂Fe(PO₄)₂.4H₂O), scholzite (CaZn₂(PO₄)₂.2H₂O), andhureaulite (Mn₅(PO₄)₂[PO₃(OH)]₂.4H₂O).
 2. The aqueous surfaceconditioner for use in a phosphating treatment according to claim 1,wherein the phosphate coating is comprised mainly of hopeite,phosphophyllite or a mixture of hopeite and phosphophyllite and thecrystals are selected from the group consisting of magnesiumhydrogenphosphate (MgHPO₄.3H₂O), zirconium oxide (ZrO₂), zinc oxalate(Zn(COO)₂), cobalt oxalate (Co(COO)₂), iron orthosilicate (Fe₂SiO₄),iron metasilicate (FeSiO₃), and magnesium borate (Mg₃(BO₃)₂) andmixtures thereof.
 3. The aqueous surface conditioner for use in aphosphating treatment according to claim 1, wherein the phosphatecoating is comprised mainly of scholzite and the crystals are selectedfrom the group consisting of anhydrous cobalt phosphate (CO₃(PO₄)₂),anhydrous zinc phosphate (γ-Zn₃(PO₄)₂), anhydrous zinc magnesiumphosphate (Zn₂Mg(PO₄)₂), anhydrous zinc cobalt phosphate(γ-Zn₂Co(PO₄)₂), anhydrous zinc iron phosphate (γ-Zn₂Fe(PO₄)₂) andmixtures thereof.
 4. The aqueous surface conditioner for use in aphosphating treatment according to claim 1, wherein the phosphatecoating is comprised mainly of hureaulite, and the crystals are one ormore types selected from the group consisting of calcium orthosilicate(Ca₂SiO₄.H₂O), calcium metaphosphate (Ca₃(PO₃)₆. 10H₂O), manganese(II)metaphosphate (Mn₃(PO₃)₆.10H₂O) and mixtures thereof.
 5. A method forconditioning a surface of a metal material, comprising contacting thesurface of the metal material with the aqueous surface conditioneraccording to any of claims 1 to 4 prior to subjecting the surface of themetal material to phosphating treatment.